The present invention relates to a water distribution and return control system for evaporative cooling pad installations of the type that are used, for example, in greenhouses, poultry houses, and livestock installations. Such evaporative cooling pad systems are usually installed within one or more of the walls of the building and utilize water soaked pads. The outside air is cooled as it passes into the building through the water soaked pads because of the vaporization of the water. A pump is employed to supply water at controlled rates to a drip conductor positioned above the pad. The water drips downwardly from the conductor through the pad soaking same. Simultaneously, exhaust fans installed within the walls of the building create a negative or partial pressure thereby causing outside air to pass through the water soaked pads into the building thereby effecting the desired cooling of the incoming air. Excess water is collected below the pad in a gutter or sump and thereafter pumped back to the drip conductor to continue the cooling operation. Originally, the pads which were used consisted of select-cut, high altitude grown aspen fibers formulated of desired density, texture and thickness and covered by plastic netting. For some time, however, the cooling pads have been constructed of cellulose paper impregnated with insoluble anti-rot salts. Such pad material is designed with a cross-fluted configuration which induces a high degree of turbulent mixing of water and air contributing to the evaporative efficiency. Additionally, the cross-fluted design of the pad material produces a strong, self-supporting pad structure which may be held firmly in place within the wall of the building. Examples of evaporative pad cooling systems such as described above include U.S. Pat. Nos. 4,389,352 and 4,031,180 of the Assignee of the present invention.
In evaporative cooling systems such as described above, water is used as the liquid being recirculated and evaporated. Water in excess of that required for the evaporation process per se, is needed to prevent scaling or salt build-up and to ensure that the evaporative cooling pads (media) are completely saturated. This excess water may be directed back to the holding tank or sump and recirculated along with fresh water as required for recirculation. Other systems supply water to the pad and thereafter direct the excess water off as waste or possibly use the water for other applications. In those systems which recirculate the water, potential problems exist, such as making provision for a large holding area for the returned and recirculating water, accommodating the build-up of minerals in the recirculated water due to the evaporation of the water and flushing of the minerals that are left back into the holding tank or sump, as well as algae growth in the holding tank and/or on the evaporative cooling pad material with resulting loss of efficiency due to mineral and/or algae build-up on the surface of the evaporative cooling pad material.
Evaporative cooling pad systems have typically employed large storage tanks or sumps, to accommodate the volume of water that was believed to be necessary for proper functioning of the entire system. The problem with large storage tanks is that the water remaining in the tank or sump after many days of operation becomes high in minerals due to the fact that the minerals in the water are not evaporated when the water in the cooling system is evaporated. Without dumping a percentage of the water, the excess mineral build-up will result in collection of minerals on the cooling pads and the eventual clogging of the pads. If water is drained off as the cooling system operates, the amount of water being drained can cause the surrounding areas to become muddy which can be a substantial inconvenience. In addition, large storage tanks also provide an ideal place for algae to grow. This algae can then spread to the cooling pads where it can clog the passages as well as producing permanent damage to the pad material. The solution to this serious problem inherent in existing systems is expensive chemicals to kill the algae in the storage tanks and in the cooling pads.
The evaporative cooling pad system of the present invention operates as a need-to-use filling system. The improved system disclosed herein recognizes that the evaporative rate of the pads is not nearly as large as the flow of water required over the pads. The system of the present invention does away with problems associated with large storage and return systems. Heretofore it was believed that storage systems were required to be quite large to make sure that there was enough water for the pump during start up and also when the system is shut down that there is enough capacity in the sump for return water from the pads.
The multi-stage distribution and return control system of the present invention eliminates the problems inherent with large storage tanks or sumps and instead uses a small sump tank. The capacity of the tank needs only to be large enough to start wetting the pads; thereafter a multi-level switch control supplies additional water when necessary. When the thermostat calls for cooling, a water valve is activated causing water to enter the sump tank until a float engages a mid-level switch. As long as the float is off the mid-level switch, the tank is continuously filled with water. As soon as the thermostat calls for cooling, the pump is activated unless the water level is below that defined by a low-level switch. The pumping operation continues until the water goes down to the point where the float disengages a low-level switch. When the low-level switch is deactivated, the pump is cut off until water fills the tank again to the mid-level mark defined by the mid-level switch. This movement back and forth from the mid-level to the low-level stabilizes as soon as the pads are totally wet. When enough water is evaporated from the pads for the water level to fall below the mid-level, the float engages the mid-level switch which activates the water valve and the tank is again filled to the mid-level point.
When the temperature of the building reaches its desirable low-level, the thermostat turns the cooling system off, i.e., the pump and the water valve are turned off. If the water returning from the pads is sufficient in volume to activate the high-level switch, a pump relay is activated which turns the pump back on. Power to the pump relay continues to be supplied through the low-level relay until the float deactivates the low-level switch at which time the pump is shut off. This wetting and stopping continues until enough water is evaporated in the pads to keep the water level in the sump tank below the high-level point.
In addition to the foregoing, there is integrated into the water distribution and return control system an automatic flush and dump system. At a pre-designated time, a flush selector switch is set on "auto" and the flush and dump cycle activated by a time clock. An auto flush relay is energized which activates the flush valve and the pump relay. The water remaining in the sump tank is pumped through the filter and out through the flush valve. This process carries the trash in the filter out the flush valve. Since the timing of the flush and drain cycle is set to occur when the thermostat has shut off the cooling system, the water valve does not come on. Water in the sump tank is pumped out until the float deactivates the low-level switch and shuts off the low-level relay. The dump valve is then energized through the low-level relay and the water remaining in the sump tank is drained out through the sump valve and related lines. A time clock then closes the dump valve at a predetermined interval. This process can be accomplished manually if the flush selector switch is turned to the "on" position.